The present invention relates to a coated cutting tool that uses a superhard blank. More specifically, the present invention pertains to a coated cutting tool that uses, for example, a brazed-in polycrystalline cubic boron nitride blank.
Heretofore, there have been known coated cutting tools that use a superhard blank as the cutting element that provides a cutting edge. These cutting tools comprise a cutting tool body that contains a notch or pocket. The superhard blank is brazed into the notch or pocket using a braze alloy so that a braze joint is formed between the superhard blank and the cutting tool body.
In one alternative, the superhard blank comprises a support (e.g. cobalt cemented tungsten carbide) on which there is a layer of superhard material (e.g. polycrystalline cubic boron nitride). As another alternative, the blank is comprised of entirely superhard material. During the material removal process, the superhard layer (or superhard material) defines a cutting edge that comes into contact with the workpiece material to remove workpiece material so as to function as a cutting element.
During the material removal operation there is generated heat (and sometimes considerable heat) at the point of contact between the cutting edge of the superhard material and the workpiece material. This is especially the case when the workpiece material is hard such as, for example, a D3 tool steel. Such a material has a hardness on the order of Rockwell C 60 (AISI D3) wherein the quenched hardness can range between about 64 to about 66 Rockwell C and the tempered hardness can range between about 54 and about 61 Rockwell C.
Because of the generation of excessive heat, the use of coated cutting tools with a brazed-in superhard blank have experienced the drawback of debrazing of the superhard blank from the cutting tool body. In other words, the heat generated at the point of contact between the superhard blank and the workpiece material passes through the superhard blank so as to cause the temperature at the braze joint to reach such a level that the braze alloy melts (or softens) thereby reducing the shear strength of the braze joint. A reduction in the shear strength of the braze joint weakens the braze joint so that the cutting forces exerted on the superhard blank can detach the superhard blank from the cutting tool body.
Dry cutting processes such as removing material by machining from carbon:carbon composite materials, abrasive-reinforced polymeric materials, and various types of wood materials through the use of cutting tools using a brazed-in superhard blank can also generate higher cutting temperatures. As mentioned earlier, these higher cutting temperatures result in a higher temperature at the braze joint. These higher temperatures at the braze joint can result in a softening or melting of the braze alloy thereby reducing the shear strength so as to cause the superhard blank to become detached or separated from the cutting tool body under the influence of the cutting forces exerted on the superhard blank.
The degree of the cutting forces exerted on the cutting tools taken in light of the cutting temperature, the temperature at the braze joint, the liquidus temperature of the braze alloy, and the shear strength of the braze alloy appear to influence the ability of the superhard blank to be retained in the pocket of the cutting tool during the material removal operation. When the temperature at the braze joint reaches a certain level, there begins a reduction in the shear strength of the braze joint. When the shear strength of the braze joint is less than necessary to maintain its integrity against the cutting forces exerted on the superhard blank, the superhard blank becomes detached from the cutting tool body. As one can appreciate, the premature (or catastrophic) separation or detachment of the superhard blank from the cutting tool body is an undesirable result.
It would thus be desirable to provide a coated cutting tool that uses a brazed-in superhard blank as the cutting element that presents a cutting edge wherein the braze joint between the cutting tool body and the superhard blank is able to withstand the heat generated during the material removal operation.
It would also be desirable to provide a coated cutting tool that uses a brazed-in superhard blank as the cutting element that presents a cutting edge wherein the braze joint between the cutting tool body and the superhard blank is able to withstand the heat generated during the material removal operation through the use of braze alloys that maintain an adequate shear strength at the temperatures that exist at the braze joint during the material removal operation (i.e., high temperature braze alloys) so as to maintain the integrity of the braze joint.
It would further be desirable to provide a coated cutting tool that uses a brazed-in superhard blank as the cutting element that presents a cutting edge wherein the braze joint between the cutting tool body and the superhard blank is able to withstand the heat generated during the material removal operation through the use of high temperature braze alloys along with the geometry and design of the superhard blank so as to reduce the exposure of the braze joint to excessive temperatures so that the integrity of the brazed joint is maintained during the material removal operation.
It would be additionally desirable to provide a coated cutting tool that uses a brazed-in superhard blank as the cutting element that presents a cutting edge wherein the braze joint between the cutting tool body and the superhard blank is able to withstand the heat generated during the material removal operation through the geometry and design of the superhard blank so as to reduce the exposure of the braze joint to excessive temperatures so that the integrity of the braze joint is maintained during the material removal operation.
Finally, it would be desirable to provide a coated cutting tool that uses a brazed-in superhard blank as the cutting element that presents a cutting edge wherein the braze joint between the cutting tool body and the superhard blank is able to withstand the heat generated during the material removal operation through the use of high temperature braze alloys as well as coating schemes that help protect the braze joint from exposure to excessive temperatures.